U.S. patent application number 12/594261 was filed with the patent office on 2010-09-23 for inverter controller, and motor driving device, electric compressor and electric home appliance using the inverter controller.
This patent application is currently assigned to Panasonic Corporation. Invention is credited to Hideharu Ogahara.
Application Number | 20100237809 12/594261 |
Document ID | / |
Family ID | 40261195 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100237809 |
Kind Code |
A1 |
Ogahara; Hideharu |
September 23, 2010 |
INVERTER CONTROLLER, AND MOTOR DRIVING DEVICE, ELECTRIC COMPRESSOR
AND ELECTRIC HOME APPLIANCE USING THE INVERTER CONTROLLER
Abstract
An inverter controller for driving a brushless DC motor, of
which rotor is provided with permanent magnets, includes an
inverter circuit, a position sensing circuit, a DC voltage sensor,
and a conduction angle controller. The inverter circuit is
connected to the brushless DC motor for driving this motor. The
position sensing circuit senses a rotor position with respect to a
stator from an induction voltage of the brushless DC motor. The DC
voltage sensor senses a voltage value of a DC power voltage
supplied to the inverter circuit. The conduction angle controller
changes a conduction angle of the inverter circuit within a range
less than 180 degrees in electric angles in response to a rate of
change in the DC power voltage.
Inventors: |
Ogahara; Hideharu; (Shiga,
JP) |
Correspondence
Address: |
RATNERPRESTIA
P.O. BOX 980
VALLEY FORGE
PA
19482
US
|
Assignee: |
Panasonic Corporation
Osaka
JP
|
Family ID: |
40261195 |
Appl. No.: |
12/594261 |
Filed: |
December 2, 2008 |
PCT Filed: |
December 2, 2008 |
PCT NO: |
PCT/JP2008/003549 |
371 Date: |
October 1, 2009 |
Current U.S.
Class: |
318/400.13 ;
318/400.34 |
Current CPC
Class: |
H02P 6/15 20160201; H02P
6/182 20130101; H02P 29/026 20130101; H02P 6/157 20160201 |
Class at
Publication: |
318/400.13 ;
318/400.34 |
International
Class: |
H02P 6/18 20060101
H02P006/18; H02P 6/14 20060101 H02P006/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2007 |
JP |
2007-318150 |
Claims
1. An inverter controller for driving a brushless DC motor having a
stator and a rotor which includes permanent magnets, the inverter
controller comprising: an inverter circuit coupled to the brushless
DC motor configured to drive the brushless DC motor; a position
sensing circuit configured to sense a position of the rotor with
respect to the stator from an induction voltage of the brushless DC
motor; a DC voltage sensor configured to sense a voltage value of a
DC power voltage supplied to the inverter circuit; and a conduction
angle controller configured to change a conduction angle of the
inverter circuit within a range from over 0 degree to less than 180
degrees in electric angles in response to a rate of change in the
DC power voltage.
2. The inverter controller according to claim 1, wherein the
conduction angle controller reduces the conduction angle in
response to the rate of change in the DC power voltage when the DC
power voltage lowers at a given rate of change or more.
3. The inverter controller according to claim 2, wherein the
conduction angle controller reduces the conduction angle at a
greater rate of change in the DC power voltage.
4. The inverter controller according to claim 1, wherein the
conduction angle controller reduces the conduction angle in
response to the rate of change in the DC power voltage when the DC
power voltage rises at a given rate of change or more.
5. The inverter controller according to claim 4, wherein the
conduction angle controller reduces the conduction angle at a
greater rate of change in the DC power voltage.
6. The inverter controller according to claim 1 further comprising
a conduction angle setting section configured to set the conduction
angle, wherein the conduction angle controller increases the
conduction angle step by step to a value set by the conduction
angle setting section when the DC power voltage stays stable.
7. A motor driving device comprising: the inverter controller as
defined in claim 1; and the brushless DC motor driven by the
inverter circuit of the inverter controller.
8. The motor driving device according to claim 7, wherein the rotor
of the brushless DC motor includes the permanent magnets embedded
therein, and has salient-pole properties.
9. The motor driving device according to claim 7, wherein the
brushless DC motor includes stator windings of which number of
turns is at least 160.
10. The motor driving device according to claim 7, wherein the
brushless DC motor has six poles or more.
11. An electric compressor comprising: the inverter controller as
defined in claim 1; the brushless DC motor driven by the inverter
circuit of the inverter controller; and a compressor section driven
by the brushless DC motor.
12. An electric home appliance comprising: the inverter controller
as defined in claim 1; the brushless DC motor driven by the
inverter circuit of the inverter controller; and a driven body
driven by the brushless DC motor.
Description
[0001] This application is a u.s. National Phase application of PCT
International Application PCT/JP2008/003549.
TECHNICAL FIELD
[0002] The present invention relates to a wide-angle conduction
control method employed in an inverter controller for a brushless
DC motor, and it also relates to motor driving devices, electric
compressors, electric home appliances such as a refrigerator, using
the inverter controller.
BACKGROUND ART
[0003] As control over the waveform of an inverter, 120-degree
conduction waveforms is generally adopted from the viewpoint of
simplicity in control. In a driving system for a brushless DC
motor, switches of respective phases of the inverter are
electrically conducted within 120 degrees in electrical angles
although the electrical angle is spanned as wide as 180 degrees
both on positive side and negative side respectively. No control is
thus done in the remaining period of 60 degrees in electrical
angles. During this non-controlled period, the inverter fails to
output a desired voltage, so that the inverter uses the DC voltage
at a low utilization rate. This low utilization rate causes a low
voltage between the respective terminals of the brushless DC motor
as well as narrows the working range of the inverter. The maximum
rotational speed of the DC motor is thus obliged to be low.
[0004] On the other hand, a wide-angle control method, which widens
an electrically conduction angle to over 120 degrees in electrical
angles, is proposed because this method allows enlarging the
working range of the inverter for increasing an output of the
inverter controller (e.g. refer to Patent citation 1, for
instance). Patent citation 1 discloses that a conduction range of a
voltage-type inverter is set at a given range over 120 degrees and
not greater than 180 degrees in electrical angles, so that a
non-controlled period becomes as small as less than 60 degrees in
electrical angles. As a result, the voltages between the respective
terminals of the motor become greater, which widens the working
range of the inverter.
[0005] In recent years, permanent magnets are embedded in a rotor
to generate torque caused by reluctance in addition to torque
caused by magnets for obtaining higher efficiency. This brushless
DC motor allows increasing the torque without a need for increasing
a motor current.
[0006] To use this reluctance torque more efficiently, a voltage
phase of the inverter is advanced with respect to an
induction-voltage phase of the motor. This is called a
phase-advancing control method, which can also efficiently use a
weak magnetic flux, thereby increasing output-torque.
[0007] A compressor employs an inverter controller which uses no
sensors such as a Hall element, from the viewpoints of service
condition, reliability and maintenance. The inverter controller
employs a sensor-less method in which a pole position of a rotor is
sensed from an induction voltage generated in stator windings. This
sensor-less method uses the span of 60 degrees in electrical
angles, i.e. the non-controlled period, and monitors induction
voltages available at the respective terminals of the motor during
the switch-off of the upper and lower arms, thereby sensing the
pole position of the rotor.
[0008] A conventional inverter controller is described hereinafter
with reference to the accompanying drawings. FIG. 7 shows a
structure of the conventional inverter, and FIG. 8 shows
characteristics of torque vs. rotational speed of the conventional
inverter. Specifically, it shows the characteristics of wide-angle
control. FIG. 8 tells that the maximum rotational speed increases
at a wider conduction angle provided when the torque is kept at a
constant level.
[0009] FIG. 9 shows timing charts of the signal waveforms of
respective sections of the conventional inverter controller. The
timing charts also indicate the processes of the respective
sections and the characteristics at conduction angle of 150 degrees
in electrical angles. In FIG. 7, three pairs of switching
transistors connected in series, i.e. Tru and Trx, Try and Try, Trw
and Trz are coupled between the terminals of DC power supply 001,
thereby forming inverter circuit 002. Brushless DC motor 003 is
formed of stator 003A and rotor 003B. Stator 003A is formed of four
poles and distributed windings. Rotor 003B is an interior magnet
type where permanent magnets 003N and 003S are embedded.
[0010] The connection points of respective pairs of the switching
transistors are coupled to brushless DC motor 003 at respective
terminals of stator windings 003U, 003V, and 003W of respective
phases, forming a "wye" connection. The connection points of
respective pairs of the switching transistors are also coupled to
respective resistors 004U, 004V, and 004W forming a "wye"
connection. Reflux diodes Du, Dx, Dv, Dy, Dw, and Dz are coupled
between the collector and the emitter of respective switching
transistors Tru, Trx, Trv, Try, Trw, and Trz, for a protection
purpose.
[0011] Pole-position sensing circuit 010 is formed of differential
amplifier 011, integrator 012, and zero-crossing comparator 013. A
voltage at neutral point 003D of stator windings 003U, 003V, and
003W coupled together in the wye connection is supplied to an
inverting input terminal of amplifier 011B via resistor 011A. A
voltage at neutral point 004D of resistors 004U, 004V, and 004W
coupled together in the wye connection is supplied directly to
non-inverting input terminal of amplifier 011B. Resistor 011C is
coupled between an output terminal and the non-inverting input
terminal of amplifier 011B. Differential amplifier 011 is thus
formed.
[0012] An output signal from the output terminal of differential
amplifier 011 is supplied to integrator 012 formed of resistor 012A
and capacitor 012B coupled together in series. An output signal
from integrator 012 (i.e. a voltage at a connection point between
resistor 012A and capacitor 012B) is supplied to a non-inverting
input terminal of zero-crossing comparator 013.
[0013] A voltage at neutral point 003D is supplied to an inverting
input terminal of zero-crossing comparator 013. An output terminal
of zero-crossing comparator 013 outputs a pole-position sensing
signal.
[0014] Differential amplifier 011, integrator 012 and zero-crossing
comparator 013 form pole-position sensing circuit 010 which senses
a pole position of rotor 003B of brushless DC motor 003.
Pole-position sensing circuit 010 outputs the pole-position sensing
signal to microprocessor 020. Microprocessor 020 then corrects the
phases of the supplied pole-position sensing signal in order to
measure a cycle, and set a phase advance angle as well as a
conduction angle. Microprocessor 020 calculates a timer counting
value per cycle of an electric angle for determining a commutation
signal of respective switching transistors Tru, Trx, Trv, Try, Trw,
and Trz.
[0015] Microprocessor 020 outputs a voltage instruction based on a
rotational speed instruction, and performs pulse width modulation
(PWM) to the voltage instruction. Microprocessor 020 controls a
duty ratio, i.e. a ratio of ON vs. OFF of a PWM signal, based on a
difference between the rotational speed instruction and an actual
rotational speed, and outputs PWM signals for the three phases.
Microprocessor 020 increases the duty ratio when the actual
rotational speed is smaller than the rotational speed instruction,
and reduces the duty ratio when the actual rotational speed is
greater than the rotational speed instruction.
[0016] The PWM signal is supplied to driving circuit 030. Driving
circuit 030 outputs driving signals to respective base terminals of
switching transistors Tru, Trx, Trv, Try, Trw, and Trz.
[0017] A conduction work of the inverter controller discussed above
is described hereinafter. In FIG. 9, induction voltages Eu, Ev, and
Ew of phases U, V and W of brushless DC motor 003 vary while the
respective phases shift by 120 degrees from each other. A
differential amplifier output signal indicates a signal output from
differential amplifier 011. A signal supplied from integrator 012
forms an integral waveform shaped by integrator 012. A supply of
the integral waveform to zero-crossing comparator 013 prompts an
output signal from zero-crossing comparator 013 to rise and then
fall at the zero-crossing point of the integral waveform. This
excitation switching signal is output as the pole-position sensing
signal.
[0018] The rise and fall of the excitation switching signal prompt
phase correction timer G1 to start, and the start of timer G1
prompts second phase correction timer G2 to start. Both of timers
G1 and G2 advance inverter mode N, i.e. a commutation pattern, by
one step.
[0019] A conduction timing of phase U can be calculated based on
the induction voltage waveform of phase W, and an amount of phase
advance of the inverter can be controlled by phase-correction timer
G1. In FIG. 9, a phase advance angle is set at 60 degrees when
conduction angle is 150 degrees in electric angles. Phase
correction timer G1 thus counts a value corresponding to 45
degrees, and second phase correction timer G2 counts a value
corresponding to 30 degrees in electric angles. As a result, the
ON-OFF states of switching transistors Tru, Trx, Trv, Try, Trw, and
Trz are controlled as shown in FIG. 9 in response to the respective
inverter modes.
[0020] As discussed above, brushless DC motor 003 can be driven in
a state where a conduction period is set between 120 degrees and
180 degrees, and a phase of inverter voltage can be advanced with
respect to that of the induction voltage of the motor.
[0021] The rotation of rotor 003B generates an induction voltage at
stator windings 003U, 003V, 003W, and the induction voltage can be
sensed through the foregoing conventional structure. This induction
voltage is shifted its phase by integrator 012 having a delay of 90
degrees, thereby sensing a position sensing signal corresponding to
a magnetic pole of rotor 003B. Based on this position sensing
signal, conduction timings to stator windings 003U, 003V, 003W are
determined. Use of such integrator 012 as having a phase-delay of
90 degrees lowers the responsiveness to an abrupt acceleration or
deceleration.
[0022] A position sensing circuit improved in responsiveness has
been proposed (e.g. refer to Patent citation 2, for instance).
Another conventional inverter controller disclosed in Patent
citation 2 is described hereinafter with reference to the
accompanying drawings. FIG. 10 shows a structure of another
conventional inverter controller, and FIG. 11 shows timing charts
of the signal waveforms of respective sections of the conventional
inverter controller. The timing charts also indicate the processes
of the respective sections.
[0023] In FIG. 10, resistors 101 and 102 are coupled in series
between bus 103 and bus 104, and their common connection point,
i.e. sensing terminal ON, supplies voltage VN of a virtual neutral
point. Voltage VN is a half of the voltage of DC power supply 001,
and the voltage of DC power supply 001 corresponds to a voltage of
the neutral point of stator windings 105U, 105V, and 105W.
[0024] Respective non-inverting input terminals (+) of comparator
106A, 106B, and 106C are coupled to output terminals OU, OV, and OW
via resistors 107, 108, and 109, respectively. Respective inverting
input terminals (-) of the comparators are coupled to sensing
terminal ON.
[0025] Respective output terminals of comparators 106A, 106B, and
106C are coupled to microprocessor 110, having a logic circuit
therein, at its input terminals 11, 12, and 13. Outputs from output
terminals 01 through 06 of microprocessor 110 drive switching
transistors Tru, Trx, Trv, Try, Trw, and Trz via driving circuit
120.
[0026] Brushless DC motor 105 includes four poles and distributed
windings. Rotor 105A forms a structure of surface mounted magnet,
i.e. permanent magnets 105N and 105S are mounted to the surface of
rotor 105A. Motor 105 is thus set in a state where conduction angle
is set at 120 degrees and phase advance angle is set at 0 degree in
electric angles.
[0027] The structure is further described with reference to FIG.
11. Terminal voltage Vu, terminal voltage Vv, and terminal voltage
Vw indicate respectively the voltages across stator windings 105U,
105V, and 105W during a regular operation of motor 105. Assume that
inverter circuit 140 supplies voltages Vua, Vva, and Vwa, and
stator windings 105U, 105V, and 105W generate induction voltages
Vub, Vvb, and Vwb. Assume that a conduction, occurring at an event
of commutation switch, of any one of reflux diodes Du, Dx, Dv, Dy,
Dw, or Dz of inverter circuit 140 will generate pulse-like spike
voltages Vuc, Vvc, and Vwc. Then respective terminal voltages Vu,
Vv, Vw form a waveform combined by supplied voltages Vua, Vva, Vwa,
induction voltages Vub, Vvb, Vwb, and spike voltages Vuc, Vvc, Vwc
respectively.
[0028] Output signals PSu, PSv, PSw from the comparators indicate
the results of comparison done by comparators 106A, 106B, 106C
between terminal voltages Vu, Vv, Vw and voltage VN at the virtual
neutral point. In this case, output signals PSu, PSv, PSw are
formed of signals PSua, PSva, PSwa which indicate a
positive-negative and a phase of each one of induction voltages
Vub, Vvb, Vwb, and output signals PSub, PSvb, PSwb corresponding to
spike voltages Vuc, Vvc, Vwc.
[0029] Spike voltages Vuc, Vvc, Vwc are neglected by a wait-timer,
so that output signals PSu, PSv, PSw indicate a positive-negative
and a phase of each one of induction voltages Vub, Vvb, Vwb, as a
result.
[0030] Microprocessor 110 recognizes six modes, A, B, C, D, E, and
F as shown in the mode column based on the status of signals PSu,
PSv, PSw output from the comparators, and then it outputs driving
signals DSu through DSz with a delay of 30 degrees in electric
angles from the instant of variation in levels of output signals
PSu, PSv, PSw. Respective time T of each mode A through F indicates
60 degrees, and a half of the time of each mode A through F, i.e.
T/2, indicates a delay time corresponding to 30 degrees in electric
angles.
[0031] Microprocessor 110 thus senses the rotational position of
rotor 105A of motor 105 based on the induction voltages generated
at stator windings 105U, 105V, 105W in response to the rotation of
rotor 105A. It also determines driving signals for the conduction
to stator windings 105U, 105V, 105W, depending on the conduction
mode and the timing, by detecting the variable time T of the
induction voltages, and then supplies electricity to stator
windings 105U, 105V, and 105W.
[0032] The foregoing structure thus differs from the conventional
inverter controller disclosed in Patent citation 1, and since it
needs no filter circuit, it can detect an induction voltage with
higher sensitivity. As a result, starting characteristic can be
improved, and the motor can be driven at a lower rotational speed.
On top of that, since no filter circuit having a delay of 90
degrees is used, the motor can be controlled with a delay of as
small as 30 degrees by combining first timer 122 and second timer
123. The responsiveness to an abrupt acceleration or deceleration
can be thus improved.
[0033] Next, out-of-synchronous characteristics of voltages and
conduction angles of an inverter controller is described
hereinafter with reference to FIG. 12. FIG. 12 shows the
out-of-synchronous characteristics of the voltages and the
conduction angles of the inverter controller shown in FIG. 10. As
FIG. 12 shows, in the case of a sharp fall of the voltage, a
resistance to the out-of-synchronous decreases at a greater
conduction angle. Characteristics similar to this one can be also
observed when the voltage sharply rises.
[0034] Patent citation 1 proposes magnetic-pole-position sensing
circuit 010 operable within a period of 180 degrees in electric
angles. However, since circuit 010 employs a filter, a delay of 90
degrees in electric angles occurs, which causes a lower
responsiveness to a variation in rotational speed such as an abrupt
change in load. As a result, the motor sometimes falls in
out-of-synchronous and halts its work.
[0035] Patent citation 2 proposes a position sensing circuit free
from a delay of 90 degrees in electric angles. However, even this
structure sometimes cannot sense the pole-position during a
rotational variation, such as an abrupt change in load, and thus
the motor may fall in out-of-synchronous. Such a phenomenon occurs
in the following cases: (1) when wide-angle control which widens a
conduction angle to over 120 degrees is carried out, (2) when
phase-advance-angle control is carried out, this control method
advances a voltage phase of the inverter with respect to a phase of
the induction voltage of the motor, (3) when a width of the spike
voltage is widened in order to obtain a higher efficiency by
increasing an inductance through a greater number of turns of
stator windings 105U, 105V, 150W. These cases incur a shorter
position sensible period.
[0036] In the case of employing a concentrated winding in a stator
of the motor in order to obtain a higher efficiency and to increase
greater torque, when six poles are used instead of four poles, the
position sensible period decreases to as small as 2/3 mechanical
angles comparing with the case of using four poles. Therefore, the
foregoing wide-angle control, the phase-advance-angle control, the
increase in the number of turns, or the increase in the number of
poles for incurring the shorter mechanical position sensible range,
shortens the pole-position sensible period. Thus an occurrence of a
variation in load, an instantaneous power interruption, or a
variation in voltage will accompany an abrupt variation in
rotation, so that the inverter controller fails to sense the pole
position and the motor falls in the out-of-synchronous.
[Patent Citation 1]
International Publication Pamphlet No. 95/27328
[Patent Citation 2]
[0037] Japanese Patent Unexamined Publication No. H01-8890
DISCLOSURE OF INVENTION
[0038] The present invention provides a reliable inverter
controller which changes instantaneously a conduction angle in
response to a change in voltage of a DC voltage section, thereby
preventing a brushless DC motor from falling in out-of-synchronous
and stopping its work due to an instantaneous power interruption or
an abrupt change in voltage. The present invention also provides
motor driving devices, electric compressors, and electric home
appliances using the inverter controller. The inverter controller
of the present invention drives a brushless DC motor, of which
rotor includes permanent magnets. The inverter controller has an
inverter circuit, a position sensing circuit, a DC voltage sensor,
and a conduction angle controller. The inverter circuit is coupled
to and drives the brushless DC motor. The position sensing circuit
senses a position of the rotor with respect to a stator from an
induction voltage of the brushless DC motor. The DC voltage sensor
senses a voltage supplied to the inverter circuit. The conduction
angle controller changes a conduction angle of the inverter circuit
in response to a rate of change in the voltage supplied from the DC
power supply within the range lower than 180 degrees in electric
angles. When a rotational speed of the motor changes due to an
abrupt change in voltage caused by, e.g. an instantaneous power
interruption, the structure described above allows reducing the
conduction angle, thereby enlarging a position sensible period. The
foregoing structure thus prevents the inverter controller from
losing the pole position of the rotor. As a result, the inverter
controller improves its responsiveness to changes in the rotational
speed caused by voltage variation, prevents the motor from falling
in the out-of-synchronous caused by the voltage variation, and
improves the resistance to the instantaneous power
interruption.
BRIEF DESCRIPTION OF DRAWINGS
[0039] FIG. 1 shows a structure of an inverter controller in
accordance with an embodiment of the present invention.
[0040] FIG. 2 is a timing chart showing waveforms of respective
sections in the inverter controller shown in FIG. 1 and the
processes done by the respective sections.
[0041] FIG. 3 shows characteristics indicating the relation between
conduction angles and variations in a power supply voltage of the
inverter controller shown in FIG. 1.
[0042] FIG. 4 is a timing chart showing operation of the inverter
controller shown in FIG. 1 when a voltage changes therein.
[0043] FIG. 5 is a block diagram of an electric compressor that
employs the inverter controller shown in FIG. 1.
[0044] FIG. 6 is schematically a sectional view of a refrigerator
as an example of electric home appliances that employ the
compressor shown in FIG. 5.
[0045] FIG. 7 shows a structure of a conventional inverter
controller.
[0046] FIG. 8 shows characteristics of torque vs. rotational speed
of the inverter controller shown in FIG. 7.
[0047] FIG. 9 is a timing chart showing waveforms of respective
sections of the inverter controller shown in FIG. 7 and the
processes done by the respective sections.
[0048] FIG. 10 shows a structure of another conventional inverter
controller.
[0049] FIG. 11 is a timing chart showing waveforms of respective
sections of the inverter controller shown in FIG. 10 and the
processes done by the respective sections.
[0050] FIG. 12 shows characteristics of out-of-synchronous caused
by the relation between voltages and conduction angles of the
inverter controller shown in FIG. 10.
BEST MODE FOR CARRYING OUT THE INVENTION
[0051] An exemplary embodiment of the present invention is
demonstrated hereinafter with reference to the accompanying
drawings. Not to mention, this embodiment does not limit the
present invention.
[0052] FIG. 1 shows a structure of an inverter controller in
accordance with this embodiment of the present invention. FIG. 2 is
a timing chart showing waveforms of respective sections in the
inverter controller and timing the processes done by the respective
sections. FIG. 3 shows characteristics indicating the relation
between conduction angles and voltage variations in a power supply
of the inverter controller. FIG. 4 is a timing chart showing
operation of the inverter controller when a voltage changes in the
inverter controller.
[0053] As shown in FIG. 1, inverter controller 200 is coupled to
commercial AC power supply 201 and brushless DC motor (hereinafter
simply referred to as "motor") 204, and drives motor 204. Inverter
controller 200 and motor 204 thus form motor driving device 300.
Motor 204 includes rotor 204B provided with permanent magnets 204C
through 240H. Inverter controller 200 includes inverter circuit
205, position sensing circuit 207, DC voltage sensor 209, and
microprocessor 208 having conduction angle controller 217.
[0054] Motor 204 has six poles and concentrated windings on salient
poles, and is formed of rotor 204B and stator 204A having
three-phase windings. Stator 204A has six poles and nine slots, and
the number of turns of respective stator windings 204U, 204V, 204W
is 189. Rotor 204B includes permanent magnets 204C through 204H
therein, and forms an interior-magnets structure which generates
reluctance torque.
[0055] Inverter controller 200 further has rectifier 203, driving
circuit 206. Rectifier 203 converts commercial AC power supply 201
into a DC power supply, and driving circuit 206 drives inverter
circuit 205.
[0056] Inverter circuit 205 is coupled to and drives motor 204, and
is formed of six switching transistors Tru, Trx, Trv, Try, Trw, and
Trz coupled together forming a three-phase bridge, and reflux
diodes Du, Dx, Dv, Dy, Dw, and Dz respectively coupled in parallel
with the switching transistors.
[0057] Position sensing circuit 207 senses a position of rotor 204B
with respect to stator 204A from an induction voltage of motor 204,
and is formed of comparators (not shown) and the like. Circuit 207
compares a terminal voltage signal based on the induction voltage
of motor 204 with a reference voltage by the comparators, thereby
outputting a position signal of rotor 204B. The structure of
circuit 207 is similar to the structure formed of comparators 106A,
106B, 106C shown in FIG. 10.
[0058] DC voltage sensor 209 senses a DC power voltage supplied to
inverter circuit 205. In other words, sensor 209 senses a voltage
converted into a DC form by rectifier 203, and forms a voltage
divider circuit using resistors. Sensor 209 outputs the sensed
voltage in the form of analog value to microprocessor 208, and it
includes a CR filter circuit for reducing noises.
[0059] Microprocessor 208 is shown with the block diagrams
including respective functions that control inverter circuit 205.
These function blocks can be formed of an exclusive circuit, or
formed of software built in hardware. To be more specific,
microprocessor 208 has rotational speed sensor 210, commutation
controller 211, duty setting section 212, PWM controller 213, drive
controller 214, and carrier outputting section 215.
[0060] Microprocessor 208 further has conduction angle controller
217 which changes a conduction angle in response to a rate of
change in the DC power voltage, and conduction angle setting
section 218 which sets the maximum value of the conduction angle.
As it will be detailed later, conduction angle controller 217
changes the conduction angle of inverter circuit 205 within the
range over 0 degree to less than 180 degrees in electric angles in
response to the rate of change in the DC power voltage.
Microprocessor 208 includes timer 219 for finding a change in
voltage per unit time, i.e. the rate of change in the DC power
voltage.
[0061] The operation and the work of above-discussed respective
function blocks of microprocessor 208 in inverter controller 200
are demonstrated hereinafter. Commutation controller 211 calculates
a timing of the commutation based on a position signal supplied
from position sensing circuit 207, and produces commutation signals
for the switching transistors Tru, Trx, Trv, Try, Trw, and Trz.
[0062] Rotational speed sensor 210 counts position signals for a
certain period, or measures pulse intervals, thereby calculating
the rotational speed of motor 204.
[0063] Duty setting section 212 makes add-subtract calculations of
a duty ratio by using a deviation between the rotational speed
obtained by rotational speed sensor 210 and an instructed
rotational speed, and supplies the duty ratio to PWM controller
213. A greater duty ratio is supplied PWM controller 213 when an
actual rotational speed is lower than the instructed rotational
speed, and a smaller duty ratio is supplied when the actual
rotational speed is higher than the instructed rotational
speed.
[0064] Carrier outputting section 215 sets a carrier frequency that
switches the switching transistors Tru, Trx, Trv, Try, Trw, and
Trz. In this embodiment, the carrier frequency is set between 3 kHz
and 10 kHz.
[0065] PWM controller 213 outputs a PWM modulated signal based on
the carrier frequency set by carrier outputting section 215 and the
duty ratio set by duty setting section 212.
[0066] Conduction angle controller 217 calculates a rate of change
in voltage per unit time with timer 219 based on the DC voltage
sensed by DC voltage sensor 209, and controls a conduction angle in
inverter circuit 205 to decrease at a greater rate of change in the
voltage. In this embodiment, conduction angle controller 217 reads
a voltage sensed by DC voltage sensor 209 at a sampling cycle, i.e.
every 5 ms, and calculates the rate of change in the DC power
voltage. When a little change in the voltages is produced and thus
controller 217 determines that no variation is found in the rate of
change, controller 217 increases the conduction angle step by
step.
[0067] Drive controller 214 compounds a commutation signal, a PWM
modulated signal, a conduction angle, and a phase advance angle,
thereby producing a driving signal, which turns on or off the
switching transistors, Tru, Trx, Trv, Try, Trw, and Trz, and
outputs this driving signal to driving circuit 206. Driving circuit
206 then turns on or off the switching transistors, Tru, Trx, Trv,
Try, Trw, and Trz, based on the driving signal, thereby driving
motor 204.
[0068] Next, various waveforms of inverter controller 200 are
described hereinafter with reference to FIG. 2. Inverter controller
200 controls motor 204 with the conduction angle set at 150 degrees
and the phase advance angle set at 15 degrees in electric angles.
Conduction angle setting section 218 sets the maximum conduction
angle at 150 degrees, and minimum conduction angle at 120
degrees.
[0069] As shown in FIG. 2, respective phases of terminal voltage Vu
across phase U, terminal voltage Vv across phase V, and terminal
voltage Vw across phase W of motor 204 shift by 120 degrees from
each other, and these phases move with this 120 degrees maintained.
Assume that inverter circuit 205 supplies voltages Vua, Vva, and
Vwa to stator windings 204U, 204V, and 204W, and these windings
generate induction voltages Vub, Vvb, and Vwb, respectively. Assume
that any one of reflux diodes Du, Dx, Dv, Dy, Dw, and Dz of
inverter circuit 205 becomes conductive at a switching event of the
commutation, thereby producing pulse-like spike voltages Vuc, Vvc,
Vwc. Then terminal voltages Vu, Vv, Vw shape waveforms which are
combined by supplied voltages Vua, Vva, Vwa, induction voltages
Vub, Vvb, Vwb, and spike voltages Vuc, Vvc, Vwc. The comparators
compare terminal voltages Vu, Vv, Vw with voltage VN at a virtual
neutral point, i.e. a half of the voltage produced by the DC power
supply, and outputs signals PSu, PSv, PSw.
[0070] In the foregoing condition, when the DC power voltage
abruptly lowers, an actual rotational speed of motor 204 lowers in
proportion to the rate of change in the DC power voltage. The
cross-point, where the induction voltage crosses voltage VN of the
virtual neutral point, fades into the conduction period. In a
similar way, when the DC power voltage abruptly rises, the actual
rotational speed of motor 204 sharply increases, and the cross
point fades into the spike voltages. Either of these events invites
an erroneous sense of pole position of the rotor, and incurs the
out-of-synchronous.
[0071] To overcome the foregoing problem, this embodiment of the
present invention, as shown in FIG. 3, allows DC voltage sensor 209
to sense a change in the DC power voltage, and allows conduction
angle controller 217 to calculate a rate of change in the DC power
voltage every 5 ms, i.e. the cycle of timer 219, thereby
determining a conduction angle. Conduction angle controller 217
decreases the conduction angle as the change in the DC power
voltage becomes greater, and also decreases the conduction angle as
a variation time becomes longer. The conduction angle is thus
changed in response to the rate of change in the DC voltage, so
that motor 204 can be more stably. As shown in FIG. 3, assume that
the rate of change in the DC power voltage is 100V/second,
200V/second, or 300V/second, and then the DC power voltage stays
stable at reference voltage E0 and at conduction angle 150 degrees
until reference time reaches "t0".
[0072] From time "t0", the DC power voltage starts varying. Since
conduction angle controller 217 senses the DC power voltage with
timer 219 every 5 ms, controller 217 can calculate the rate of
change in the voltages at point "t1", "t2", "t3", and onward at
intervals of every 5 ms.
[0073] In this embodiment, the minimum resolution of the conduction
angle is set at 3.75 degrees in electrical angles, so that when the
rate of change is 100V/second, the conduction angle decreases by
3.75 degrees every 10 ms, and in the case of 200V/second, it
decreases by 3.75 degrees every 5 ms, and in the case of
300V/second, it decreases by 11.25 degrees in 10 ms.
[0074] Next, the operation of inverter controller 200 during a
variation in voltages, e.g. during an instantaneous power
interruption, is described with reference to FIG. 4. When motor 204
is in an initial state, motor 204 is under a heavy load and rotates
at a high rotational speed. When an abrupt fall of the DC power
voltage occurs (Step 1), conduction angle controller 217 reduces
the conduction angle from 150 degrees to 127.5 degrees in response
to the rate of change in the DC power voltage. The reduction in the
conduction angle allows enlarging the position sensible period, so
that position sensing circuit 207 will not lose the pole position
of the rotor in the conduction period. As a result, the
out-of-synchronous due to a change in voltages can be
prevented.
[0075] In the next case, after the abrupt fall of the DC power
voltage, the DC power voltage stays steadily at a low voltage (Step
2). In this condition, conduction angle controller 217 widens the
conduction angle step by step (every 100 ms), and then after a
lapse of 500 ms, the conduction angle increases from 127.5 degrees
to 142.5 degrees. In this case, the output becomes low due to a low
voltage, so that a wider conduction angle is needed for increasing
the output. Conduction angle controller 217 thus tries to increase
the angle to the maximum angle, i.e. 150 degrees. In other words,
when the DC power voltage is stable, conduction angle controller
217 increases the conduction angle step by step to the value set by
conduction angle setting section 218. In such a case, since no
variation in the rotation occurs, wide-angle operation is
achievable, and the conduction angle can be restored to the given
value when the voltage becomes stable. As a result, motor 204 can
work again at a high rotational speed and produce again large
torque.
[0076] When the DC voltage sharply rises from the stable condition
(Step 3), conduction angle controller 217 changes the conduction
angle from 142.5 degrees to 120 degrees. In other words, when the
DC power voltage rises at a given rate of change or over that given
rate, controller 217 reduces the conduction angle in response to
the rate of change in the DC power voltage. This is similar to the
case when the DC power voltage sharply falls. The position sensible
period thus can be enlarged, so that position sensing circuit 207
will not lose the pole position of the rotor in the spike voltage.
As a result, motor 204 is prevented from falling in the
out-of-synchronous caused by the change in rotation due to an
increase in voltage.
[0077] When the DC power voltage varies up and down (Step 4),
conduction angle controller 217 controls the conduction angle to
decrease. When conduction angle stays at 120 degrees in electric
angles and the DC power voltage still varies (Step 5), conduction
angle controller 217 maintains the conduction angle at 120 degrees,
i.e. the minimum set value.
[0078] When the DC power voltage steadily stays at a high voltage
(Step 6), conduction angle controller 217 increases the conduction
angle to the given value, i.e. 150 degrees (maximum set value).
However, since the high voltage allows outputting high power, the
maximum set value can be as small as 120 degrees.
[0079] The maximum conduction angle can be set in response to the
duty ratio, rotational speed, and DC power voltage.
[0080] In this embodiment, rotor 204B employs interior permanent
magnets 204C through 204H, and has salient-pole properties, so that
motor 204 can produce reluctance torque. In this case, a phase
advance control is carried out in order to efficiently use the
reluctance torque; however, use of this phase advance control
together with the wide-angle control will further reduce the
position sensible period. This embodiment yet proves that the phase
advance control in addition to the wide-angle control will reduce
events of the out-of-synchronous caused by changes in voltage, so
that the resistance to the instantaneous power interruption can be
increased.
[0081] Use of stator 204A having a greater number of turns will
increase the inductance, thereby widening the width of the spike
voltage, so that the position sensible period decreases. To be more
specific, in the case of over 160 turns of the stator winding, this
phenomenon appears conspicuously. However, this embodiment prevents
such a motor from falling in the out-of-synchronous caused by
changes in voltage, so that the resistance to the instantaneous
power interruption can be increased.
[0082] Motor 204 having six poles or more than six poles is obliged
to encounter a difficulty of sensing a rotor position comparing
with a conventional motor having four poles, because the increase
in the number of poles reduces the position sensible period due to
an issue of mechanical angle. However, this embodiment prevents
motor 204 having six poles or more than six poles from falling in
the out-of-synchronous caused by changes in voltage, so that the
resistance to the instantaneous power interruption can be
increased.
[0083] In this embodiment, the conduction angles changes from 150
degrees to 120 degrees step by step through nine steps; however,
the rate of change in the DC power voltage and the conduction angle
can be changed linearly, and a sampling cycle of the DC power
voltage can be set at any value. On top of that, use of the
conduction angle less than 120 degrees will make the system more
resistible to the changes in power voltage or the instantaneous
power interruption.
[0084] As shown in FIG. 5, inverter controller 200 and motor 204
form motor driving device 300, and motor driving device 300 and
compressing section 400 form electric compressor 500. Motor driving
device 300 drives compressing section 400, which is a driven body.
Compressor 500 thus can prevent motor 204 from falling in the
out-of-synchronous caused by changes in voltage, and it also can
make motor 204 more resistible to the instantaneous power
interruption, thereby increasing the reliability. In addition, as
shown in FIG. 6, electric home appliances, such as refrigerators,
can use compressor 500, or motor driving device 300 can be used for
driving a motor of washing machines. In the later case, a pulsator
or a rotary drum is driven by motor driving device 300. The use of
motor driving device 300 in electric home appliances discussed
above assures excellent operation of the appliances.
INDUSTRIAL APPLICABILITY
[0085] The inverter controller of the present invention can sense a
magnetic pole position of the rotor without losing the pole
positions of the rotor even if a change in the power voltage
occurs. The inverter controller is useful in electric home
appliances such as air-conditioners, refrigerators, and washing
machines and electric vehicles encountering changes in the power
voltage. It is also useful in the regions where changes in the
power voltage often occur.
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